A young woman was in a serious condition in hospital today after leaping on to a freight train in London ad being burnt by live overhead cables.

The 22-year-old sparked an explosion by touching the 25,000-volt wires and was thrown 20ft on to the platform where her friends had stood watching, the London Evening Standard reported.

Her actions were branded a “moment of madness” as rail chiefs warned the public against copycat stunts.

Witnesses told the Standard that the woman, who appeared intoxicated, removed her high heels before climbing onto the carriage of the train as it waited at Hackney Wick station in east London on Wednesday night.

She spent 15 minutes dodging between the carriages, even stopping to pose spread-eagled while laughing to her friends below.

However, an explosion, accompanied by a bright flash of light, caused the woman to fall backwards on to the platform. Her condition today was described as serious but stable.

A witness, who didn’t want to be named, told the Standard: “We saw her climb up from a ladder at the side of one of the carriages and thought, ‘This girl is an idiot’. We all thought it was stupid, madness, and that she was going to get arrested.

“She looked wasted and was clambering about up there, then it was like a bright flash of light with sparks and parts of her clothes were on fire.

“Then she just froze for a couple of seconds and went super-stiff and fell on to the platform. The flash hurt your eyes. It went from that to fire.

“I think she might have ended up between the wires and then went into one of them. The explosion was so loud you couldn’t hear if she screamed or said anything at all. The whole thing probably lasted about 15 minutes.

“We ran over to the other side of the platform where she was and couldn’t believe she was conscious and breathing. We thought she’d be dead.”

Other rail users rushed to the woman’s aid while a group of friends stayed with her until ambulance crews arrived and rushed her to hospital.

Network Rail said: “The railway is a dangerous place, with trains travelling at high speeds and power lines carrying more than 25,000 volts of electricity. What might have seemed a harmless prank very nearly ended in tragedy.”

British Transport Police said an investigation was continuing. A spokeswoman said: “Officers were called to Hackney Wick station at 11.06pm to a report a woman had been injured.

“It is believed the woman, who fell from the roof of a train, came into contact with electricity from the overhead power lines.

“Officers are now working to establish how she came to be on the train.”